2. Materials and methods
In this study, it is assumed that renewable sugars produced from OPF will be transported to the centralized biorefinery plant for P(3HB) production from at least 10 palm oil mills within a 80 km radius that have similar capacity to process oil palm fresh fruit bunch (FFB) at 200,000 t/y as previously reported by Zahari et al. (2014). Additionally, it is assumed that the biorefinery plant will be located at one of the 10 mills to utilize the surplus energy from the palm oil mill. Fig. 1 shows the proposed diagram of integrated OPF renewable sugars and biorefinery plant for the production of P(3HB).
Proposed diagram of integrated OPF renewable sugars and biorefinery plant for ...
Fig. 1.
Proposed diagram of integrated OPF renewable sugars and biorefinery plant for the production of P(3HB) and bioethanol.
Figure options
2.1. Basis of the proposal
As a basis for economic analysis, the production cost of P(3HB) was estimated based on the potential amount of renewable sugars that can be produced from OPF in a year from 10 palm oil mills. The fresh OPF will be pressed in the mill, whereby OPF fibre will be saccharified to obtain additional renewable sugars (mainly glucose). The renewable sugars produced are partially concentrated by evaporation and transported to a centralized biorefinery plant to be used as a fermentation feedstock for P(3HB) and bioethanol production.
Due to constraints in the transportation cost, and to benefit from the economy scale, we propose only one biorefinery plant processing renewable sugars from OPF to produce P(3HB) from among the 10 palm oil mills. Fresh fronds (petiole section only) are collected in the plantations during harvesting of the FFB, transported to the mill and subsequently pressed in the mill to obtain the renewable sugars. The pressed OPF fibre will be saccharified to obtain more renewable sugars. Therefore, several costs are involved in the renewable sugars production from OPF, including transportation, harvesting and collection of OPF from the oil palm plantation to the mill. Additionally, the cost of enzymes used for the saccharification of OPF fibre is also included.
Renewable sugars produced from each mill will be concentrated and transported to a centralized biorefinery plant for P(3HB) production. We propose the distance between the centralized biorefinery plant and each of the palm oil mills to be not more than 80 km, as shown in Fig. 1.
2.2. Renewable sugars production cost
In this study, the major costs contributing heavily to the total production cost of renewable sugars from OPF are transportation, harvesting and collection cost of OPF from the oil palm plantation to the mill, pre-processing cost and the cost of enzymes used for the saccharification of OPF fibre. All prices used in this study were determined based on the current situation in Malaysia and valued in US Dollar ($).
2.2.1. Description of the process
We have previously reported that 50% (wt/wt) of OPF juice could be obtained from fresh OPF by using a simple sugarcane pressing machine (Zahari et al., 2012a). To obtain the OPF juice at an industrial scale, we proposed the use of a compressing sap system that was developed by Murata et al. (2013). In their report, they use a compressing sap system to obtain the saps containing sugars from the oil palm trunk (OPT). As OPT can be pressed due to its high sugar content, it was postulated that the same process can be performed on OPF. Apart from OPF juice, pressed OPF fibre was also produced as a by-product of the OPF pressing process. Pressed OPF fibre contains a substantial amount of carbohydrate, which is also useful as fermentation feedstock (Zahari et al., 2014). As shown in Fig. 2, there are two avenues for producing sugars from OPF. Firstly, sugars in the OPF juice could be obtained by pressing the fresh OPF using a compressing sap system. The OPF juice is filtered to remove solid particles, evaporated to reduce the content of water and finally stored in a storage tank prior to use as fermentation substrate for P(3HB) production. Secondly, the OPF pressed fibre undergoes a physical-mechanical pre-treatment before being hydrolysed to glucose and xylose by saccharification using 20 FPU of cellulase (Meiji Seika), as previously explained in Zahari et al. (2014). Based on the report, maximum glucose and xylose concentrations of 0.469 g and 0.298 g, respectively per g of OPF petiole could be obtained from the saccharification method with 95% of holocellulose being converted into mixed sugars (Zahari et al., 2014). The mixture of sugars comprising glucose and xylose is separated by nanofiltration method as reported by Sjöman et al. (2007). Finally, the separated product, which is glucose mixed with OPF juice is used as fermentation feedstock for P(3HB) production, while xylose is used as feedstock for bioethanol production. The overall mass balance for the production of renewable sugars from OPF is presented in Fig. 2.
Overall mass balance for the production of renewable sugars from oil palm frond ...
Fig. 2.
Overall mass balance for the production of renewable sugars from oil palm frond (OPF) from 10 palm oil mills.
Figure options
2.2.2. Transportation cost
Current cost estimates, based on the density of the product and the distance of transportation, range from about $ 0.067 to 3.33/(t km) (MIA, 2011). The average transport cost in Malaysia is taken to be $ 10/t for a 100 km distance as quoted by The Malaysian Transport Association. As a basis for calculation, the transportation cost was estimated at $ 10/t OPF processed for less than 100 km distance.
2.2.3. Harvesting and collection cost of oil palm frond
The OPF is obtained during harvesting of FFB. Currently, cut fronds are left as topsoil replacement and natural fertilizer (MIA, 2011). Different methods could be adopted to collect the fronds, ranging from simple manual collection with a wheelbarrow, collection with a buffalo cart or a motorized cart, to advanced mechanization. The choice of collection method for a specific plantation depends on the terrain (e.g., elevation, spacing of trees), labour constraints and economy of scale. Depending on the collection method, cost estimates range from $ 5.33–22.33/t (dry mass basis) ( MIA, 2011). As a basis for calculation, the cost for harvesting and collection of OPF was estimated at $ 10/t OPF.
2.2.4. Pre-processing cost
Different biomass types can undergo different forms of pre-processing in order to reduce the moisture content, reduce the weight or volume to be transported and/or in preparation for a specific end use (MIA, 2011). For instance, trunks and fronds can be chipped, dried and/or pelletised, while OPEFB and mesocarp fibre can be shredded, dried and/or compacted. Palm kernel shells already have very low moisture content and thus can be used or transported without further pre-processing. Depending on the type of biomass and the extent of pre-processing required, cost estimates range from $ 5–180/t for mesocarp fibres, fronds, trunks and OPEFB (MIA, 2011). With drying accounting for a large proportion of pre-processing cost, it is likely that both plantations and downstream industries will explore scenarios that do not require biomass to be dried. Since fresh OPF was used in this case study, there will be no drying process required. Therefore, the pre-processing cost was estimated at $ 5/t OPF.
2.2.5. Cost of enzymes for saccharification process
The cost of enzymes for saccharifying lignocellulosic biomass has dramatically decreased over the past decade by approximately 20-fold (MacMillan et al., 2011). Currently, the cost of enzymes is estimated at approximately $ 0.04 to 0.07/kg glucose. As a basis for calculation, the cost of enzymes for saccharification of OPF fibre to obtain renewable sugars (glucose and xylose) is estimated at $ 20/t OPF fibre processed (Lee and Ofori-Boateng, 2013).
2.3. Poly(3-hydroxybutyrate) production cost
As a basis for calculation, the data for cost estimation were taken from the integrated production of biodegradable plastic, sugar and ethanol from sugarcane, which was reported by Nonato et al. (2001). In this case study, Cupriavidus necator NCIMB 11599 (mutant strain of H16) was used for the production of P(3HB) using renewable sugars from OPF and the data for the fermentation process were reported earlier in Zahari et al. (2014). For the P(3HB) extraction and purification process, a similar method reported by Muhammadi et al. (2012) was proposed in this case study. The NaOH digestion method, which resulted in a recovery efficiency of more than 95%, was employed for the recovery of P(3HB). Purification steps were accomplished by using ethanol and water. The use of non-organic, non-halogenated solvent is favourable for PHA production and recovery at large scale as it not only minimizes the overall production cost but also eliminates tedious wastewater treatment steps afterwards ( Muhammadi et al., 2012).
2. Materials and methodsIn this study, it is assumed that renewable sugars produced from OPF will be transported to the centralized biorefinery plant for P(3HB) production from at least 10 palm oil mills within a 80 km radius that have similar capacity to process oil palm fresh fruit bunch (FFB) at 200,000 t/y as previously reported by Zahari et al. (2014). Additionally, it is assumed that the biorefinery plant will be located at one of the 10 mills to utilize the surplus energy from the palm oil mill. Fig. 1 shows the proposed diagram of integrated OPF renewable sugars and biorefinery plant for the production of P(3HB).Proposed diagram of integrated OPF renewable sugars and biorefinery plant for ...Fig. 1. Proposed diagram of integrated OPF renewable sugars and biorefinery plant for the production of P(3HB) and bioethanol.Figure options2.1. Basis of the proposalAs a basis for economic analysis, the production cost of P(3HB) was estimated based on the potential amount of renewable sugars that can be produced from OPF in a year from 10 palm oil mills. The fresh OPF will be pressed in the mill, whereby OPF fibre will be saccharified to obtain additional renewable sugars (mainly glucose). The renewable sugars produced are partially concentrated by evaporation and transported to a centralized biorefinery plant to be used as a fermentation feedstock for P(3HB) and bioethanol production.Due to constraints in the transportation cost, and to benefit from the economy scale, we propose only one biorefinery plant processing renewable sugars from OPF to produce P(3HB) from among the 10 palm oil mills. Fresh fronds (petiole section only) are collected in the plantations during harvesting of the FFB, transported to the mill and subsequently pressed in the mill to obtain the renewable sugars. The pressed OPF fibre will be saccharified to obtain more renewable sugars. Therefore, several costs are involved in the renewable sugars production from OPF, including transportation, harvesting and collection of OPF from the oil palm plantation to the mill. Additionally, the cost of enzymes used for the saccharification of OPF fibre is also included.Renewable sugars produced from each mill will be concentrated and transported to a centralized biorefinery plant for P(3HB) production. We propose the distance between the centralized biorefinery plant and each of the palm oil mills to be not more than 80 km, as shown in Fig. 1.2.2. Renewable sugars production costIn this study, the major costs contributing heavily to the total production cost of renewable sugars from OPF are transportation, harvesting and collection cost of OPF from the oil palm plantation to the mill, pre-processing cost and the cost of enzymes used for the saccharification of OPF fibre. All prices used in this study were determined based on the current situation in Malaysia and valued in US Dollar ($).2.2.1. Description of the processWe have previously reported that 50% (wt/wt) of OPF juice could be obtained from fresh OPF by using a simple sugarcane pressing machine (Zahari et al., 2012a). To obtain the OPF juice at an industrial scale, we proposed the use of a compressing sap system that was developed by Murata et al. (2013). In their report, they use a compressing sap system to obtain the saps containing sugars from the oil palm trunk (OPT). As OPT can be pressed due to its high sugar content, it was postulated that the same process can be performed on OPF. Apart from OPF juice, pressed OPF fibre was also produced as a by-product of the OPF pressing process. Pressed OPF fibre contains a substantial amount of carbohydrate, which is also useful as fermentation feedstock (Zahari et al., 2014). As shown in Fig. 2, there are two avenues for producing sugars from OPF. Firstly, sugars in the OPF juice could be obtained by pressing the fresh OPF using a compressing sap system. The OPF juice is filtered to remove solid particles, evaporated to reduce the content of water and finally stored in a storage tank prior to use as fermentation substrate for P(3HB) production. Secondly, the OPF pressed fibre undergoes a physical-mechanical pre-treatment before being hydrolysed to glucose and xylose by saccharification using 20 FPU of cellulase (Meiji Seika), as previously explained in Zahari et al. (2014). Based on the report, maximum glucose and xylose concentrations of 0.469 g and 0.298 g, respectively per g of OPF petiole could be obtained from the saccharification method with 95% of holocellulose being converted into mixed sugars (Zahari et al., 2014). The mixture of sugars comprising glucose and xylose is separated by nanofiltration method as reported by Sjöman et al. (2007). Finally, the separated product, which is glucose mixed with OPF juice is used as fermentation feedstock for P(3HB) production, while xylose is used as feedstock for bioethanol production. The overall mass balance for the production of renewable sugars from OPF is presented in Fig. 2.Overall mass balance for the production of renewable sugars from oil palm frond ...Fig. 2. Overall mass balance for the production of renewable sugars from oil palm frond (OPF) from 10 palm oil mills.Figure options2.2.2. Transportation costCurrent cost estimates, based on the density of the product and the distance of transportation, range from about $ 0.067 to 3.33/(t km) (MIA, 2011). The average transport cost in Malaysia is taken to be $ 10/t for a 100 km distance as quoted by The Malaysian Transport Association. As a basis for calculation, the transportation cost was estimated at $ 10/t OPF processed for less than 100 km distance.2.2.3. Harvesting and collection cost of oil palm frondThe OPF is obtained during harvesting of FFB. Currently, cut fronds are left as topsoil replacement and natural fertilizer (MIA, 2011). Different methods could be adopted to collect the fronds, ranging from simple manual collection with a wheelbarrow, collection with a buffalo cart or a motorized cart, to advanced mechanization. The choice of collection method for a specific plantation depends on the terrain (e.g., elevation, spacing of trees), labour constraints and economy of scale. Depending on the collection method, cost estimates range from $ 5.33–22.33/t (dry mass basis) ( MIA, 2011). As a basis for calculation, the cost for harvesting and collection of OPF was estimated at $ 10/t OPF.2.2.4. Pre-processing cost
Different biomass types can undergo different forms of pre-processing in order to reduce the moisture content, reduce the weight or volume to be transported and/or in preparation for a specific end use (MIA, 2011). For instance, trunks and fronds can be chipped, dried and/or pelletised, while OPEFB and mesocarp fibre can be shredded, dried and/or compacted. Palm kernel shells already have very low moisture content and thus can be used or transported without further pre-processing. Depending on the type of biomass and the extent of pre-processing required, cost estimates range from $ 5–180/t for mesocarp fibres, fronds, trunks and OPEFB (MIA, 2011). With drying accounting for a large proportion of pre-processing cost, it is likely that both plantations and downstream industries will explore scenarios that do not require biomass to be dried. Since fresh OPF was used in this case study, there will be no drying process required. Therefore, the pre-processing cost was estimated at $ 5/t OPF.
2.2.5. Cost of enzymes for saccharification process
The cost of enzymes for saccharifying lignocellulosic biomass has dramatically decreased over the past decade by approximately 20-fold (MacMillan et al., 2011). Currently, the cost of enzymes is estimated at approximately $ 0.04 to 0.07/kg glucose. As a basis for calculation, the cost of enzymes for saccharification of OPF fibre to obtain renewable sugars (glucose and xylose) is estimated at $ 20/t OPF fibre processed (Lee and Ofori-Boateng, 2013).
2.3. Poly(3-hydroxybutyrate) production cost
As a basis for calculation, the data for cost estimation were taken from the integrated production of biodegradable plastic, sugar and ethanol from sugarcane, which was reported by Nonato et al. (2001). In this case study, Cupriavidus necator NCIMB 11599 (mutant strain of H16) was used for the production of P(3HB) using renewable sugars from OPF and the data for the fermentation process were reported earlier in Zahari et al. (2014). For the P(3HB) extraction and purification process, a similar method reported by Muhammadi et al. (2012) was proposed in this case study. The NaOH digestion method, which resulted in a recovery efficiency of more than 95%, was employed for the recovery of P(3HB). Purification steps were accomplished by using ethanol and water. The use of non-organic, non-halogenated solvent is favourable for PHA production and recovery at large scale as it not only minimizes the overall production cost but also eliminates tedious wastewater treatment steps afterwards ( Muhammadi et al., 2012).
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